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Radio Navigation > Chapter 1 Basic Radio Theory > Flashcards

Chapter 1 Basic Radio Theory Flashcards

1
Q

Define a hertz

A

1 complete cycle (1 Hz = 1 wave per second)

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2
Q

Define the wavelength

A

The distance between a peak and the next peak

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3
Q

Define phase

A

The difference in angle between to waves

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4
Q

What is the frequency range of very low frequency (VLF)?

A

3khz - 30khz

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5
Q

What is frequency of low frequency (LF)?

A

30khz - 300khz

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6
Q

What is the frequency range if medium frequency (MF)?

A

300khz - 3mhz

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7
Q

What is the frequency range of high frequency (HF)?

A

3mhz - 30mhz

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8
Q

What is the frequency range of very high frequency (VHF)?

A

30mhz - 300mhz

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9
Q

What is the frequency range of ultra high frequency (UHF)?

A

300mhz - 3ghz

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10
Q

What is the frequency range of super high frequency (SHF)?

A

3ghz - 30ghz

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11
Q

What is the frequency range of extremely high frequency (EHF)?

A

30 ghz - 300ghz

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12
Q

What is the speed of light?

A

300,000,000 m/s (3*10^6)
300,000 km/s
162,000 nm/s

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13
Q

What is the formula relation frequency, speed of light and wavelength?

A

F = c/lambda

F = frequency (Hz)
c = speed of light
Lambda = wavelength (metres)
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14
Q

What is modulation?

A

The process of adding intelligence or information to a carrier wave

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15
Q

What are the four types of modulation?

A

Pulse modulation/keying, amplitude, frequency and phase

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16
Q

What does phase modulation require?

A

A complex demodulator

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17
Q

Where is phase modulation used?

A

In GPS receivers

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18
Q

What does modulation create?

A

Upper and lower frequency known as side bands (e.g. a modulation of 2Hz creates a bandwidth of 4Hz)

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19
Q

Why are single side bands used for HF comms?

A

Reduces the requirement for the power needed to transmit the signal

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20
Q

What are the 6 types of antennas?

A

Dipole, loop, parabolic, phases array, slotted planar array and helical

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21
Q

What is the orientation of the magnetic (H) field and the electric (E) field on a vertical antenna?

A 
Magnetic = horizontal
Electric = vertical
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22
Q

What is the most basic antenna?

A

A dipole antenna

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23
Q

What does a dipole antenna consist of?

A

Two unipole antennas

24
Q

How much does each pole contribute to the total wavelength?

A

One quarter (so dipole = half of the wavelength)

25
Q

What are the three categories of radio waves?

A

Ground, sky and space waves

26
Q

Where is the weakest reception on a dipole antenna?

A

Directly above it

27
Q

Define diffraction

A

The ability of a radio wave to follow the curvature of the earth

28
Q

How does diffraction vary with frequency?

A

The lower the frequency the greater the diffraction

29
Q

Define attenuation

A

How much a radio wave deteriorates (high attenuation is bad)

30
Q

What is the main propagation method of HF radio waves?

A

Sky waves (still some ground waves)

31
Q

What is the relationship between frequency and refraction?

A

The lower the frequency the greater the refraction

32
Q

How does a radio wave react when it meets the ionosphere?

A

It refracts (IT DOES NOT REFLECT)

33
Q

Why don’t VHF waves diffract?

A

Too low frequency

34
Q

What is the attenuation like of VHF waves?

A

Very high attenuation

35
Q

What are the three alternative names for VHF waves?

A

Line of sight waves, space waves and direct waves

36
Q

How does attenuation vary with frequency?

A

The lower the frequency the lower attenuation

37
Q

How does the ionosphere density change during the course of 24 hours?

A 
Day = higher density
Night = lower density
38
Q

What radio waves does the D layer have no effect on?

A

HF and above

39
Q

What are the two layers in the F layer?

A

F1 and F2

40
Q

What frequencies pass through the F layer?

A

UHF and above

41
Q

Beyond the ionosphere how does attenuation vary with frequency?

A

Higher frequency = less attentuation

42
Q

What layer of the ionosphere do HF refract off?

A

The F layer

43
Q

What happens to the D layer at night?

A

It disappears

44
Q

What happens to the E layer at night?

A

Moves higher up

45
Q

What happens to the F layer at night?

A

They merge into one

46
Q

What happens to both the E and F laters at night?

A

Become thinner and less dense

47
Q

What happens to the amount of refraction at night?

A

Refraction reduces due to the lower density of the layers

48
Q

How are radio waves frequencies changed at night?

A

Lower the frequency

49
Q

During the day what waves does VLF produce?

A

Ground and sky waves

50
Q

During the night what waves does VLF produce?

A

Ground waves

51
Q

What is the critical angle sky wave?

A

The min angle at which the radio wave will refract and return to earth

52
Q

What is the skip distance?

A

Distance between the transmitter and the point where the first sky wave arrives

53
Q

What is the dead space area?

A

Area between the limit of the ground waves and the first sky wave

54
Q

How is the dead space area reduced?

A

Reduce frequency

55
Q

How is the critical angle reduced?

A

Lower frequency

56
Q

What causes super refraction?

A

A temperature inversion and/or rapid decrease in humidity with height

57
Q

What are is the effect of super refraction?

A

Unexpected VHF ranges

Radio Navigation (11 decks)

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